AC motor control apparatus

ABSTRACT

A control apparatus for an AC motor includes a current sensor and an estimation section. The current sensor detects current flowing through one phase of the motor. The estimation section repeats an estimation process. In the estimation process, d-axis and q-axis current estimation values are calculated based on the presently detected current of the one phase and a previous current estimation value of another phase of the motor, and a present current estimation value of each phase is calculated based on smoothed values of the d-axis and q-axis current estimation values. The estimation section performs the estimation process based on a phase lag element. The phase lag element is a difference between the presently detected current and a previous current estimation value of the one phase or the previously detected current.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2012-97221 filed on Apr. 22, 2012, the contents of which are incorporated herein by reference.

FIELD

The present disclosure relates to a control apparatus for controlling a three-phase AC motor by using a current sensor that detects an electric current flowing through one of three phases of the AC motor.

BACKGROUND

In recent years, from social demands for low-fuel consumption and low exhaust emission, there has been an increased attention to an electric vehicle or a hybrid vehicle which has an alternate-current (AC) motor to run. For example, in a hybrid vehicle, an AC motor is connected to a direct-current (DC) power source such as a rechargeable battery unit through a power converter such as an inverter. The inverter converts a DC voltage supplied from the DC power source to an AC voltage and drives the AC motor with the AC voltage.

A typical control system for controlling an AC motor mounted on an electric vehicle or a hybrid vehicle uses two or three current sensors to detect two or three of three phases of the AC motor. The AC motor is controlled based on outputs (i.e., current detection values) of the current sensors. In this type of motor control system, two or three current sensors are provided to one AC motor. Therefore, the size and cost of the control system may be increased.

U.S. Pat. No. 6,229,719 corresponding to JP-A-2001-145398 discloses a technique for reducing the number of current sensors in an AC motor control system, thereby reducing the cost of the AC motor control system. In the technique, one current sensor is provided to detect a current flowing through one (e.g., U-phase) of three phases of an AC motor. A d-axis current estimation value (i.e., exciting current element estimation value) and a q-axis current estimation value (i.e., torque current element estimation value) in a rotating coordinate system of the AC motor are calculated based on the detected current and the previous current estimation values of the other phases (e.g., V-phase and W-phase). Each of the d-axis current estimation value and the q-axis current estimation value is averaged by the first-order lag filter. The present current estimation values of the other phases are calculated based on the averaged values. The AC motor is controlled by using the q-axis current estimation value (or both the d-axis current estimation value and the q-axis current estimation value).

The technique disclosed in U.S. Pat. No. 6,229,719 uses one current sensor for one AC motor, thereby reducing the size and cost of the inverter. However, depending on operation conditions, it may be difficult or impossible to ensure adequate current estimation accuracy of the AC motor. As a result, accuracy of output torque may be reduced, current control may become unstable, and torque variation may occur. Further, abnormal current or voltage may occur, and the AC motor and the inverter may be broken due to the abnormal current or voltage. Therefore, it is important to ensure adequate current estimation accuracy of the AC motor. In particular, since the electric vehicle and the hybrid vehicle have various operation conditions including a stopped condition, a high-speed running condition, a no-driving force output condition, and a rated torque output condition of the AC motor, it is very important to ensure adequate current estimation accuracy of the AC motor.

SUMMARY

In view of the above, it is an object of the present disclosure to provide a control apparatus for increasing current estimation accuracy in an AC motor by using a current sensor that detects an electric current flowing through one of phases of the AC motor.

According to an aspect of the present disclosure, a control apparatus for controlling a three-phase AC motor includes a current sensor and a current estimation section. The current sensor detects electric current flowing through one phase of the AC motor. The one phase is defined as a sensor phase. The current estimation section repeatedly performs a current estimation process in a predetermined cycle. In the current estimation process, a d-axis current estimation value and a q-axis current estimation value in a rotating coordinate system of the AC motor are calculated based on a present current detection value of the sensor phase and a previous current estimation value of another phase of the AC motor. The present current detection value is defined as the current presently detected by the current sensor. In the current estimation process, a present current estimation value of each of the sensor phase and the other phase of the AC motor is calculated based on a smoothed d-axis current estimation value and a smoothed q-axis current estimation value into which the d-axis current estimation value and the q-axis current estimation value are respectively smoothed. The current estimation section performs the current estimation process based on a phase lag element of the sensor phase. The phase lag element of the sensor phase is a difference between the present current detection value and one of a previous current estimation value of the sensor phase and a previous current detection value of the sensor phase. The previous current detection value is defined as the current previously detected by the current sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a block diagram of a hybrid vehicle driving system according to an embodiment of the present disclosure;

FIG. 2 is a block diagram of an AC motor control system according to the embodiment;

FIG. 3 is a block diagram explaining a current feedback control of an AC motor according to the embodiment;

FIG. 4 is a block diagram of a current estimation section according to the embodiment;

FIG. 5 is a flow chart of a current estimation routine according to the embodiment;

FIG. 6 is a diagram illustrating behaviors of d-axis and q-axis current estimation values calculated by current estimation according to the embodiment;

FIG. 7 is a block diagram explaining current estimation according to a comparison example;

FIG. 8 is a diagram illustrating behaviors of d-axis and q-axis current estimation values calculated by the current estimation according to the comparison example;

FIG. 9 is a diagram illustrating characteristics of a sine wave;

FIGS. 10A and 10B are diagrams illustrating a relationship between a constant value k and a stationary error; and

FIG. 11 is a block diagram of an electric vehicle driving system according to a modification of the embodiment.

DETAILED DESCRIPTION

The present inventors conducted an experiment to determine whether a motor control system that employs the technique disclosed in U.S. Pat. No. 6,229,719 can accurately estimate a d-axis current value and a q-axis current value. The experiment was started from an initial state where a d-axis current estimation value and a q-axis current estimation value are zero under a condition that the d-axis current value and the q-axis current value are kept constant. In the system used in the experiment, the d-axis current estimation value and the q-axis current estimation value are calculated based on a current, which is detected by a current sensor, of one of phases of an AC motor and the previous current estimation values of the other phases of the AC motor, and then the current estimation values of the other phases are calculated based on smoothed values of the d-axis current estimation value and the q-axis current estimation value. FIGS. 8A and 8B show a result of the experiment. As shown in FIGS. 8A and 8B, in the system, when a rotation speed of an AC motor becomes higher, the current estimation values deviate in a direction in which a phase lag becomes larger and a current absolute value becomes smaller. That is, the experiment result indicates that a stationary estimation error increases with an increase in the rotation speed of the AC motor.

After a deeply study on the experiment result, the present inventors found out that the increase in the stationary estimation error is caused by a phase lag of the previous current estimation values of the other phases used to calculate the d-axis current estimation value and the q-axis current estimation value. Specifically, the current estimation values of the other phases are in synchronism with a rotation angle of the AC motor. The rotation angle changes between the previous process and the present process. Therefore, the previous current estimation values of the other phases lag in phase by the change in the rotation angle with respect to the current value, which is presently detected by the current sensor, of the one phase. Therefore, when the d-axis current estimation value and the q-axis current estimation value are calculated by dq transformation based on the presently detected current value of the one phase and the previously estimated current values of the other phases, an estimation error occurs due to the phase lag between the current detection value of the one phase and the current estimation values of the other phases. The estimation error is not corrected and results in a stationary estimation error.

An embodiment of the present disclosure based on the above study is described below with reference to the drawings. Throughout the embodiment, the term “current” means “electric current”. In other words, the term “current” does not mean “present”.

A driving system of a hybrid vehicle according to an embodiment of the present disclosure is described below with reference to FIG. 1. An internal-combustion engine 1, a first alternating-current (AC) motor 13A, and a second AC motor 13B are mounted on the vehicle. Wheels 2 of the vehicle are driven by driving force of the second AC motor 13B and driving force that is transmitted to a rotating shaft of the second AC motor 13B by driving the first AC motor 13A against an output of the engine 1. A crankshaft of the engine 1, a rotating shaft of the first AC motor 13A, and the rotating shaft of the second AC motor 13B are coupled together through a mechanical power distribution mechanism 3 (e.g., planetary gear mechanism). The rotating shaft of the second AC motor 13B is coupled through a differential reduction gear 4 to an axle 5 of the vehicle. The AC motors 13A and 13B are connected to a direct-current (DC) power source 11, such as a rechargeable battery unit, through a motor controller 6. The motor controller 6 includes an inverter 12 (refer to FIG. 2) and a motor controlling circuit 16 (refer to FIG. 2). The AC motors 13A and 13B are supplied with electrical power from the DC power source 11 through the motor controller 6.

A driving force calculator 7 is provided by a computer that performs overall control of the vehicle. The driving force calculator 7 detects operating conditions of the vehicle based on signals received from sensors and switches. For example, the driving force calculator 7 can detect the operating conditions based on a brake signal from a brake sensor (not shown), an accelerator signal from an accelerator sensor (not shown), and a shift signal from a shift switch (not shown). The driving force calculator 7 exchanges control signals and data signals with an engine controller (not shown), which controls operations of the engine 1, and a motor controlling circuit 16 (refer to FIG. 2), which controls operations of the AC motors 13A and 13B. The driving force calculator 7 outputs a driving force command according to the operation conditions of the vehicle, thereby controlling driving forces of the engine 1 and the AC motors 13A and 13B.

Next, an AC motor control system mounted on the vehicle is described with reference to FIG. 2. It is noted that a motor control system for controlling the AC motor 13A is substantially identical to a motor control system for controlling the AC motor 13B. For the sake of simplicity, the AC motors 13A and 13B are hereinafter collectively referred to as the “AC motor 13”, and a motor control system for controlling the AC motor 13 is described below.

The inverter 12 is connected to the DC power source 11. The inverter 12 is a voltage-controlled three-phase inverter. The AC motor 13 is driven by the inverter 12. A boost converter (i.e., step-up converter) can be interposed between the DC power source 11 and the inverter 12.

The AC motor 13 is a permanent magnet three-phase synchronous motor having a permanent magnet built in a rotor. The AC motor 13 includes a rotor position sensor 14 for detecting a rotation position of the rotor. The AC motor 13 is provided with one current sensor 15 for detecting an electric current flowing through one (hereinafter referred to as the “sensor phase”) of phases of the AC motor 13. According to the embodiment, the sensor phase is a W phase, and the current sensor 15 detects the current flowing though the W phase of the AC motor 13.

The inverter 12 converts a DC voltage to three phase AC voltages U, V, and W based on leg voltage command signals UU, UL, VU, VL, WU, and WL outputted from the motor controlling circuit 16. The leg voltage command signal UU is applied to an upper switch of a U-phase leg of the inverter 12. The leg voltage command signal UL is applied to a lower switch of the U-phase leg. The leg voltage command signal VU is applied to an upper switch of a V-phase leg of the inverter 12. The leg voltage command signal VL is applied to a lower switch of the V-phase leg. The leg voltage command signal WU is applied to an upper switch of a W-phase leg of the inverter 12. The leg voltage command signal WL is applied to a lower switch of the W-phase leg.

The motor controlling circuit 16 performs torque control. In the torque control, the motor controlling circuit 16 adjusts the AC voltage applied to the AC motor 13 by controlling the inverter 12 in such a manner that an output torque of the AC motor 13 can be equal to a target torque (i.e., torque command value). Specifically, in the torque control, the motor controlling circuit 16 performs current feedback control. In the current feedback control, energization of the AC motor 13 is feedback-controlled so that a deviation between a current command value, which depends on the torque command value, and a current estimation value, which depends on an output of the current sensor 15, can be reduced. The current feedback control is described in detail below.

As shown in FIG. 3, the motor controlling circuit 16 calculates a command current vector (i.e., d-axis current command value id* and a q-axis current command value iq*), which is defined in a rotating coordinate system (i.e., dq coordinate system) set as a rotor coordinate system of the AC motor 13, based on a torque command value trq* by using a mapping table, a formula, or the like.

Further, the motor controlling circuit 16 calculates an electrical angle eθ based on a rotor rotation position mθ of the AC motor 13 detected by the rotor position sensor 14. Further, a current estimation section 17 of the motor controlling circuit 16 calculates an estimated current vector (i.e., d-axis current estimation value id.est and a q-axis current estimation value iq.est), which are defined in the rotating coordinate system, based on the electrical angle eθ and a current detection value iw.sns detected by the current sensor 15. The current detection value indicates the current flowing though the sensor phase (i.e. W-phase) of the AC motor 13.

Then, a d-axis voltage command value Vd is calculated, for example, by proportional-integral (PI) control, so that a deviation Δid between the d-axis current command value id* and the d-axis current estimation value id.est can be reduced. Further, a q-axis voltage command value Vq is calculated, for example, by PI control, so that a deviation Δiq between the q-axis current command value iq* and the q-axis current estimation value iq.est can be reduced. In this way, a command voltage vector (i.e., the d-axis voltage command value Vd and the q-axis voltage command value Vq) is calculated.

Then, three-phase voltage command values Vu, Vv, and Vw are calculated based on the command voltage vector (i.e., the d-axis voltage command value Vd and the q-axis voltage command value Vq) and the electrical angle eθ. Then, the three-phase voltage command values Vu, Vv, and Vw are converted to the leg voltage command signals UU, UL, VU, VL, WU, and WL, for example, by sinusoidal PWM control or square wave control. Then, the leg voltage command signals UU, UL, VU, VL, WU, and WL are outputted to the inverter 12. In this way, the motor controlling circuit 16 performs the current feedback control so that the energization of the AC motor 13 can be feedback-controlled in such a manner that the deviations between the current command values id* and iq*, which depend on the torque command value, and the current estimation values id.est and iq.est, which depend on the output of the current sensor 15, can be reduced, respectively.

FIG. 7 shows a system according to a comparison example studied by the present inventors. The system repeatedly performs a current estimation process in a predetermined cycle to estimate current estimation values iu.est and iv.est of the other phases (i.e., U-phase and V-phase). In the current estimation process, the d-axis current estimation value id.est and the q-axis current estimation value iq.est are calculated based on the current detection value iw.sns, which is detected by the current sensor 15, of the sensor phase (i.e., W-phase) and the previous current estimation values iu.est and iv.est of the other phases (i.e., U-phase and V-phase). Then, the d-axis current estimation value id.est and the q-axis current estimation value iq.est are smoothed by LPF processing, and the current estimation values iu.est and iv.est are calculated based on the smoothed values. The LPF processing is a process using a low-pass filter. Examples of the LPF processing can include an averaging process and a first-order lag process. In this system, although the d-axis current estimation value id.est and the q-axis current estimation value iq.est are calculated from the current detection value iw.sns and the previous current estimation values iu.est and iv.est, the previous current estimation values iu.est and iv.est lag in phase behind the current detection value iw.sns.

Therefore, the influence of the phase-lag of the previous current estimation values iu.est and iv.est with respect to the current detection value iw.sns becomes larger as the current frequency (i.e., motor rotation speed) becomes higher. Accordingly, as shown in (a), (b), and (c) of FIG. 8, a stationary error (i.e., estimation error) of the d-axis current estimation value id.est and the q-axis current estimation value iq.est with respect to an actual value becomes larger so that current estimation accuracy can be reduced. In FIG. 8, (a) shows a first case where a time constant of the LPF processing (i.e., the number of times the averaging process or the first-order lag process is performed) is large, (b) shows a second case where the time constant of the LPF processing is medium, and (c) shows a third case where the time constant of the LPF processing is small.

To overcome the above disadvantage, the present inventors focus attention on the following characteristics of a sine wave. In FIG. 9, (1) represents a waveform of a reference sine wave, (2) represents a waveform that lags in phase by a predetermined amount behind the reference waveform (1), (3) represents a waveform obtained by subtracting the reference waveform (1) from the waveform (2), and (4) represents a waveform obtained by subtracting the waveform (3) from the reference waveform (1). Since the waveform (3) is a difference between the reference waveform (1) and the waveform (2) that lags in behind the reference waveform (1), the waveform (3) can be considered as a phase lag element that causes a phase lag. In other words, since the reference waveform (1) advances in phase with respect to the waveform (2), an inversion of the waveform (3) can be considered as a phase advance element that causes a phase advance. Specifically, the waveform (4) is an addition of the inversion of the waveform (3) to the reference waveform (1) and advances in phase with respect to the reference waveform (1).

Based on the above characteristics, the present inventors consider that, in the system for controlling AC current in the AC motor 13, a phase lag element can be calculated based on a difference between a present value and a previous value having a phase lag. Further, the present inventors consider that a reduction in estimation accuracy due to phase mismatch can be reduced by adding an inversion of the phase lag element to the present value to advance phase.

For example, the present value is a present current detection value iw.sns that is presently detected by the current sensor 15, and, the previous value is a previous current estimation value iw.est of the sensor phase (i.e., W-phase). In the comparison example shown in FIG. 7, like the current estimation values iu.est and iv.est of the other phases, the current estimation value iw.est of the sensor phase can be calculated by inverse dq transformation based on the smoothed values of the d-axis current estimation value id.est and the q-axis current estimation value iq.est.

A difference (hereinafter sometimes referred to as the “current estimation error”) between the present current detection value iw.sns of the sensor phase and the previous current estimation value iw.est of the sensor phase is calculated as a phase lag element, and a current estimation value is corrected based on the phase lag element. The present inventors conclude that this approach removes the stationary error due to the phase lag of the previous current estimation values iu.est and iv.est so that the reduction in the current estimation accuracy can be prevented.

Based on the above study findings, according to the embodiment, as shown in FIG. 4, the current estimation section 17 repeatedly performs current estimation in a predetermined calculation cycle. In the current estimation, the d-axis current estimation value id.est and the q-axis current estimation value iq.est are calculated based on the current detection value iw.sns, which is detected by the current sensor 15, of the sensor phase (i.e., W-phase) and the previous current estimation values iu.est and iv.est of the other phases (i.e., U-phase and V-phase). Then, the current estimation values iu.est, iv.est, and iw.est of all phases (i.e., U-phase, V-phase, and W-phase) are calculated based on a smoothed d-axis current estimation value id.lpf and a smoothed q-axis current estimation value iq.lpf into which the d-axis current estimation value id.est and the q-axis current estimation value iq.est are respectively smoothed by the LPF processing (e.g., averaging process or a first-order lag process).

Specifically, in the current estimation, the d-axis current estimation value id.est and the q-axis current estimation value iq.est are corrected based on a current estimation error Δiw which is calculated from the current estimation value iw.est and the current detection value iw.sns of the sensor phase (i.e., W-phase). Then, the corrected d-axis current estimation value id.est and the corrected q-axis current estimation value iq.est are respectively smoothed by the LPF processing into the smoothed d-axis current estimation value id.lpf and the smoothed q-axis current estimation value iq.lpf, and the current estimation values iu.est, iv.est, and iw.est of all phases (i.e., U-phase, V-phase, and W-phase) are calculated based on the smoothed d-axis current estimation value id.lpf and the smoothed q-axis current estimation value iq.lpf.

Thus, the current estimation error Δiw of the sensor phase is calculated from the current estimation value iw.est and the current detection value iw.sns of the sensor phase, and the d-axis current estimation value id.est and the q-axis current estimation value iq.est are corrected by using the current estimation error Δiw. In such an approach, an estimation error, which is caused by a phase lag of the previous current estimation values iu.est and iv.est with respect to the current detection value iw.sns, involved in the d-axis current estimation value id.est and the q-axis current estimation value iq.est can be reduced. Accordingly, an estimation error involved in the current estimation values iu.est, iv.est, and iw.est of all phases can reduced, because the current estimation values iu.est, iv.est, and iw.est of all phases are calculated from the corrected d-axis current estimation value id.est and the corrected q-axis current estimation value iq.est.

According to the embodiment, the current estimation error Δiw of the sensor phase is calculated as a difference between the current estimation value iw.est and the current detection value iw.sns of the sensor phase. That is, Δiw=iw.est-iw.sns. Then, a d-axis current correction value id.crr and a q-axis current correction value iq.crr in a rotating coordinate system of the AC motor are calculated based on the current estimation error Δiw. Then, the d-axis current estimation value id.est is corrected by using a product of the d-axis current correction value id.crr and a constant value k. Likewise the q-axis current estimation value iq.est is corrected by using a product of the q-axis current correction value iq.crr and the constant value k. Although, the constant value k can be freely designed, it is preferable that the constant value k is 2 or a value (e.g., about 1.97) slightly less than 2. A reason for this is that the correction value needs to be doubled to correct phase lags of two phase elements (i.e., U-phase and V-phase) by one phase element (i.e., W-phase). (5) of FIG. 9 shows a waveform obtained by adding the doubled correction value to the reference waveform (1). In practice, there is a possibility that a difference in amplitude and advance in phase is not doubled exactly when the doubled corrected value is added. Therefore, it is preferable that the constant value k is slightly less than 2. FIGS. 10A and 10B are diagrams illustrating a relationship between the constant value k and the stationary error. As shown in FIGS. 10A and 10B, the stationary error occurs when the constant value k is inadequately set. Therefore, it is important to adequately set the constant value k to a specific value.

The above-described current estimation is performed by the motor controlling circuit 16 in accordance with a current estimation routine shown in FIG. 5. The current estimation routine is described below.

During an ON-period of the motor controlling circuit 16, the motor controlling circuit 16 repeatedly executes the current estimation routine in a predetermined calculation cycle. The current estimation routine starts at S101, where the motor controlling circuit 16 reads the current detection value iw.sns, which is detected by the current sensor 15, of the sensor phase (i.e., W-phase).

Then, the current estimation routine proceeds to S102, where the motor controlling circuit 16 reads the previous current estimation values iu.est and iv.est of the other phases (i.e., U-phase and V-phase).

It is noted that the inverter 12 still remains OFF immediately after the motor controlling circuit 16 is powered ON. Therefore, when the current estimation routine is executed for the first time after the motor controlling circuit 16 is powered ON, predetermined initial values are used as the previous current estimation values iu.est and iv.est. According to the embodiment, each of the initial values of the previous current estimation values iu.est and iv.est is zero.

Then, the current estimation routine proceeds to S103, where the motor controlling circuit 16 reads the electrical angle eθ, which is calculated based on the rotor rotation position mθ detected by the rotor position sensor 14.

Then, the current estimation routine proceeds to S104, where the motor controlling circuit 16 calculates the d-axis current estimation value id.est and the q-axis current estimation value iq.est by dq transformation based on the current detection value iw.sns and the previous current estimation values iu.est and iv.est. In the dq transformation, the d-axis current estimation value id.est and the q-axis current estimation value iq.est are calculated by using the following formula (1):

$\begin{matrix} {\begin{bmatrix} {{id}.{est}} \\ {{iq}.{est}} \end{bmatrix} = {\begin{bmatrix} {\cos\left( {e\;\theta} \right)} & {\cos\left( {{e\;\theta} - {120{^\circ}}} \right)} & {\cos\left( {{e\;\theta} + {120{^\circ}}} \right)} \\ {- {\sin\left( {e\;\theta} \right)}} & {- {\sin\left( {{e\;\theta} - {120{^\circ}}} \right)}} & {- {\sin\left( {{e\;\theta} + {120{^\circ}}} \right)}} \end{bmatrix}\begin{bmatrix} {{iu}.{est}} \\ {{iv}.{est}} \\ {{iw}.{sns}} \end{bmatrix}}} & (1) \end{matrix}$

Alternatively, at S104, the motor controlling circuit 16 can calculate the d-axis current estimation value id.est and the q-axis current estimation value iq.est by dq transformation based on the current detection value iw.sns of the sensor phase (i.e., W-phase) and one of the previous current estimation values of the other phases (i.e., U-phase and V-phase). For example, when the d-axis current estimation value id.est and the q-axis current estimation value iq.est are calculated based on the current detection value iw.sns of the sensor phase (i.e., W-phase) and the previous current estimation value iu.est of the U-phase, the following formula (2) is used in the dq transformation:

$\begin{matrix} {\begin{bmatrix} {{id}.{est}} \\ {{iq}.{est}} \end{bmatrix} = {{\sqrt{2}\begin{bmatrix} {\sin\left( {{e\;\theta} + {120{^\circ}}} \right)} & {- {\sin\left( {e\;\theta} \right)}} \\ {\cos\left( {{e\;\theta} + {120{^\circ}}} \right)} & {- {\cos\left( {e\;\theta} \right)}} \end{bmatrix}}\begin{bmatrix} {{iu}.{est}} \\ {{iw}.{sns}} \end{bmatrix}}} & (2) \end{matrix}$

Then, the current estimation routine proceeds to S105, where the motor controlling circuit 16 outputs the present d-axis current estimation value id.est and the present q-axis current estimation value iq.est. For example, the d-axis current estimation value id.est and the q-axis current estimation value iq.est, which are outputted at S105, can be used in the current feedback control.

Then, the current estimation routine proceeds to S106, where the motor controlling circuit 16 calculates a current estimation error Δiw which is a difference between the current estimation value iw.est and the current detection value iw.sns of the sensor phase (i.e., W-phase). That is, Δiw=iw.est-iw.sns.

Then, the current estimation routine proceeds to S107, where the motor controlling circuit 16 calculates a d-axis current correction value id.crr and a q-axis current correction value iq.crr by dq transformation using the following formula (3):

$\begin{matrix} \begin{matrix} {\begin{bmatrix} {{id}.{crr}} \\ {{iq}.{crr}} \end{bmatrix} = {\begin{bmatrix} {\cos\left( {e\;\theta} \right)} & {\cos\left( {{e\;\theta} - {120{^\circ}}} \right)} & {\cos\left( {{e\;\theta} + {120{^\circ}}} \right)} \\ {- {\sin\left( {e\;\theta} \right)}} & {- {\sin\left( {{e\;\theta} - {120{^\circ}}} \right)}} & {- {\sin\left( {{e\;\theta} + {120{^\circ}}} \right)}} \end{bmatrix}\begin{bmatrix} 0 \\ 0 \\ {\Delta\;{iw}} \end{bmatrix}}} \\ {= {\begin{bmatrix} {\cos\left( {{e\;\theta} + {120{^\circ}}} \right)} \\ {- {\sin\left( {{e\;\theta} + {120{^\circ}}} \right)}} \end{bmatrix}\Delta\;{iw}}} \end{matrix} & (3) \end{matrix}$

Then, the current estimation routine proceeds to S108, where the motor controlling circuit 16 corrects the d-axis current estimation value id.est by using a product of the d-axis current correction value id.crr and a constant value k as follows: id.est=id.est−k×id.crr. Likewise at S108, the motor controlling circuit 16 corrects the q-axis current estimation value iq.est by using a product of the q-axis current correction value iq.crr and the constant value k as follows: iq.est=iq.est−k×iq.crr. As mentioned previously, it is preferable that the constant value k is about 2.

Then, the current estimation routine proceeds to S109, the motor controlling circuit 16 performs the LPF processing so that the corrected d-axis current estimation value id.est and the corrected q-axis current estimation value iq.est can be respectively smoothed into a smoothed d-axis current estimation value id.lpf and a smoothed q-axis current estimation value iq.lpf. Then, the current estimation routine proceeds to S110, where the motor controlling circuit 16 calculates the current estimation values iu.est, iv.est, and iw.est of all phases (i.e., U-phase, V-phase, and W-phase) by inverse dq transformation based on the smoothed d-axis current estimation value id.lpf and the smoothed q-axis current estimation value iq.lpf. For example, in the inverse dq transformation, the current estimation values iu.est, iv.est, and iw.est of all phases can be calculated from the following formula (4):

$\begin{matrix} {\begin{bmatrix} {{iu}.{est}} \\ {{iv}.{est}} \\ {{iw}.{est}} \end{bmatrix} = {{\sqrt{\frac{2}{3}}\begin{bmatrix} {\cos\left( {e\;\theta} \right)} & {- {\sin\left( {e\;\theta} \right)}} \\ {\cos\left( {{e\;\theta} - {120{^\circ}}} \right)} & {- {\sin\left( {{e\;\theta} - {120{^\circ}}} \right)}} \\ {\cos\left( {{e\;\theta} + {120{^\circ}}} \right)} & {- {\sin\left( {{e\;\theta} + {120{^\circ}}} \right)}} \end{bmatrix}}\begin{bmatrix} {{id}.{lpf}} \\ {{iq}.{lpf}} \end{bmatrix}}} & (4) \end{matrix}$

Then, the current estimation routine proceeds to S111, where the motor controlling circuit 16 stores the current estimation values iu.est, iv.est, and iw.est of all phases in a buffer (i.e., data storage area). After S111, the current estimation routine is ended. The current estimation values stored in the buffer are used as the previous current estimation values when the current estimation routine is executed next time (i.e., when the current estimation is performed next time).

As described above, according to the embodiment, attention is drawn to the fact that the current estimation error Δiw of the sensor phase (i.e., W-phase) can be calculated from the current estimation value iw.est and the current detection value iw.sns of the sensor phase, and the d-axis current estimation value id.est and the q-axis current estimation value iq.est are corrected by using the current estimation error Δiw of the sensor phase. In such an approach, the estimation error, which is caused by the phase lag of the previous current estimation values iu.est and iv.est with respect to the current detection value iw.sns, involved in the d-axis current estimation value id.est and the q-axis current estimation value iq.est can be reduced. Accordingly, the estimation error involved in the current estimation values iu.est, iv.est, and iw.est of all phases (i.e., U-phase, V-phase, and W-phase) can reduced, because the current estimation values iu.est, iv.est, and iw.est of all phases are calculated from the corrected d-axis current estimation value id.est and the corrected q-axis current estimation value iq.est.

Therefore, even when the current frequency (i.e., motor rotation speed) becomes high, the influence of the phase-lag of the previous current estimation values iu.est and iv.est with respect to the current detection value iw.sns is maintained small. Accordingly, as shown (a), (b), and (c) of FIG. 6, a stationary error (i.e., estimation error) of the d-axis current estimation value id.est and the q-axis current estimation value iq.est with respect to an actual value is maintained small so that the accuracy of the d-axis current estimation value id.est, the q-axis current estimation value iq.est, and the current estimation values iu.est, iv.est, and iw.est of all phases can be increased. In FIG. 6, (a) shows a first case where a time constant of the LPF processing (i.e., the number of times the averaging process or the first-order lag process is performed) is large, (b) shows a second case where the time constant of the LPF processing is medium, and (c) shows a third case where the time constant of the LPF processing is small.

In this way, according to the embodiment, the current estimation accuracy of the AC motor 13 can be improved while satisfying the demand for the reduction in size and cost of the inverter by using one current sensor 15 in one AC motor 13. Further, as can be seen by comparing FIG. 6 and FIG. 8, as long as the time constant of the LPF processing is the same, responsiveness of the d-axis current estimation value id.est and the q-axis current estimation value iq.est is higher in the present embodiment than the comparison example in which the correction process is not performed.

Further, according to the embodiment, the energization of the AC motor 13 is feedback controlled based on the d-axis current estimation value id.est and the q-axis current estimation value iq.est that are calculated with an increased accuracy. In such an approach, a reduction in accuracy of output torque of the AC motor 13 is prevented so that the current feedback control can be stabilized.

Further, according to the embodiment, since the energization of the AC motor 13 is feedback-controlled based on the d-axis current estimation value id.est and the q-axis current estimation value iq.est that are directly estimated. In such an approach, electrical second-order variation in output torque due to a difference in gain between multiple current sensors can be perfectly prevented in principle. Specifically, the electrical second-order variation is caused by the fact that the d-axis and q-axis current values vibrate at an electrical second-order frequency.

As described above, according to the embodiment, even when one current sensor 15 is used in one AC motor 13, the reduction in accuracy of the current estimation is reduced so that the torque variation (e.g., electrical first-order variation due to a direct current element of three-phase current) can be reduced. Thus, vibration of an apparatus to which an AC motor control system that uses one current sensor in one AC motor is applied is reduced. Therefore, the embodiment can be effectively applied to AC motors, in particular, an AC motor mounted on a vehicle to provide comfortable ride and high driving performance of the vehicle.

Further, according to the embodiment, in the correction process, the current estimation error Δiw of the sensor phase is calculated as the difference between the current estimation value iw.est and the current detection value iw.sns of the sensor phase. Then, the d-axis current correction value id.crr and the q-axis current correction value iq.crr in a rotating coordinate system of the AC motor 13 are calculated based on the current estimation error Δiw. Then, the d-axis current estimation value id.est and the q-axis current estimation value iq.est are corrected by using the d-axis current correction value id.crr and the q-axis current correction value iq.crr, respectively. In this way, the d-axis current estimation value id.est and the q-axis current estimation value iq.est in a rotating coordinate system of the AC motor 13 can be corrected based on the current estimation error Δiw of the sensor phase by a simple method.

(Modifications)

While the present disclosure has been described with reference to embodiments thereof, it is to be understood that the disclosure is not limited to the embodiments and constructions. The present disclosure is intended to cover various modification and equivalent arrangements. In addition, while the various combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the present disclosure.

In the embodiment, the previous current estimation value iw.est of the sensor phase is used as a previous value having a phase lag. Thus, the correction is performed based on not only a phase lag element but also an estimation error element. Therefore, the estimation error is positively removed so that responsiveness of the current estimation can be improved (i.e., the current estimation value can converge to an actual value more rapidly). Alternatively, the previous current detection value iw.sns of the sensor phase can be used as a previous value having a phase lag. That is, the current estimation error Δiw can be calculated as a difference between the previous current detection value iw.sns and the present current detection value iw.sns of the sensor phase. In such an approach, the correction is performed based on only the phase lag element. Thus, the sensitivity of the correction to motor current distortion and noise on the current detection value is reduced so that the operation of the AC motor 13 can be stabilized.

Whether or not the previous current detection value iw.sns of the sensor phase is used as a previous value having a phase lag can be selected according to operating conditions of the AC motor 13. For example, in an unsteady condition where the torque command value will change sharply, from the standpoint of the responsiveness, it is preferable that the previous current estimation value iw.est of the sensor phase be used as a previous value. In contrast, in a steady condition where the torque command value will remain unchanged, from the standpoint of the stability, it is preferable that the previous current detection value iw.sns of the sensor phase be used as a previous value.

In the embodiment, the current estimation error Δiw is calculated from the present current detection value iw.sns as a present value and the previous current estimation value iw.est (or the previous current detection value iw.sns) as a previous value, and then the d-axis current estimation value id.est and the q-axis current estimation value iq.est are corrected by using the d-axis current correction value id.crr and the q-axis current correction value iq.crr which are calculated by dq transformation based on the current estimation error Δiw. Alternatively, the current detection value of the sensor phase can be directly corrected, when the d-axis current estimation value id.est and the q-axis current estimation value iq.est are calculated based on the current detection value iw.sns of the sensor phase and the previous current estimation values iu.est and iv.est. Specifically, the d-axis current estimation value id.est and the q-axis current estimation value iq.est can be calculated based on a corrected current detection value iw.csns of the sensor phase and the previous current estimation values iu.est and iv.est of the other phases. The corrected current detection value iw.csns is given by iw.csns=iw.sns−k×Δiw. In such an approach, there is no need to separate the dq transformation to calculate the d-axis and q-axis current estimation values from the inverse dq transformation to calculate the d-axis and q-axis current correction values. Thus, a processing load and a calculation error can be reduced.

In summary, in the current estimation, the present current detection value iw.sns can be corrected to the corrected current detection value iw.csns based on the current estimation error Δiw which is calculated from the present current detection value iw.sns and the previous current estimation value iw.est, and the d-axis current estimation value id.est and the q-axis current estimation value iq.est can be calculated based on the corrected current detection value iw.csns and the previous current estimation values iu.est and iv.est. In this case, the current estimation error Δiw can be calculated as the difference between the present current detection value iw.sns and the previous current estimation value iw.est.

Alternatively, in the current estimation, the d-axis current estimation value id.est and the q-axis current estimation value iq.est can be corrected based on the current estimation error Δiw which is calculated from the present current detection value iw.sns and the previous current detection value iw.sns, and the current estimation values iu.est, iv.est, and iw.est of all phases can be calculated based on the corrected d-axis current estimation value id.est and the corrected q-axis current estimation value iq.est. In this case, the current estimation error Δiw can be calculated as the difference between the present current detection value iw.sns and the previous current detection value iw.sns, and the d-axis current estimation value id.est and the q-axis current estimation value iq.est can be corrected by using the d-axis current correction value id.crr and the q-axis current correction value iq.crr which are calculated based on the current estimation error Δiw.

Alternatively, in the current estimation, the present current detection value iw.sns can be corrected to the corrected current detection value iw.csns based on the current estimation error Δiw which is calculated from the present current detection value iw.sns and the previous current detection value iw.sns, and the d-axis current estimation value id.est and the q-axis current estimation value iq.est can be calculated based on thee corrected current detection value iw.csns and the previous current estimation values iu.est and iv.est of the other phases. In this case, the current estimation error Δiw can be calculated as the difference between the present current detection value iw.sns and the previous current detection value iw.sns.

In the embodiment, the current estimation error Δiw of the sensor phase is calculated as the difference between the current estimation value iw.est and the current detection value iw.sns of the sensor phase. The current estimation error Δiw of the sensor phase can be calculated in another way. For example, the current estimation error Δiw of the sensor phase can be calculated as a ratio between the current estimation value iw.est and the current detection value iw.sns of the sensor phase.

In the embodiment, the d-axis current estimation value id.est and the q-axis current estimation value iq.est are corrected based on the current estimation error of the sensor phase. Alternatively, the smoothed d-axis current estimation value id.lpf and the smoothed q-axis current estimation value iq.lpf, into which the d-axis current estimation value id.est and the q-axis current estimation value iq.est are respectively smoothed by the LPF process, can be corrected based on the current estimation error of the sensor phase.

In the embodiment, the sensor phase is the W-phase. Alternatively, the sensor phase can be the U-phase or the V-phase.

In the embodiment, the current feedback control of the AC motor 13 is performed based on the d-axis current estimation value id.est and the q-axis current estimation value iq.est to increase accuracy and responsiveness of the current feedback control. Alternatively, the current feedback control can be performed based on the smoothed d-axis current estimation value id.lpf and the smoothed q-axis current estimation value iq.lpf.

In such an approach the sensitivity of the current feedback control to motor current distortion and noise on the current detection value is reduced so that the operation of the AC motor 13 can be stabilized.

Whether or not the current feedback control is performed based on the smoothed current estimation values can be selected according to operating conditions of the AC motor 13. For example, in an unsteady condition where the torque command value will change sharply, it is preferable that the current feedback control of the AC motor 13 be performed based on the d-axis current estimation value id.est and the q-axis current estimation value iq.est. In contrast, in a steady condition where the torque command value will remain unchanged, it is preferable that the current feedback control of the AC motor 13 be performed based on the smoothed d-axis current estimation value id.lpf and the smoothed q-axis current estimation value iq.lpf.

The present disclosure can be applied also to a driving system of an electric vehicle such as shown in FIG. 11. Specifically, in the driving system of the electric vehicle shown in FIG. 11, the wheels 2 of the electric vehicle are driven by driving force of an AC motor 13. The AC motor 13 is connected to the DC power source 11, such as a rechargeable battery unit, through the motor controller 6. The motor controller 6 includes the inverter 12 (refer to FIG. 2) and the motor controlling circuit 16 (refer to FIG. 2). The AC motor 13 is supplied with electrical power from the DC power source 11 through the motor controller 6.

The driving force calculator 7 is provided by a computer that performs overall control of the electric vehicle. The driving force calculator 7 detects operating conditions of the electric vehicle based on signals received from sensors and switches. For example, the driving force calculator 7 can detect the operating conditions based on the brake signal from the brake sensor (not shown), the accelerator signal from the accelerator sensor (not shown), and the shift signal from the shift switch (not shown). The driving force calculator 7 exchanges control signals and data signals with the motor controlling circuit 16 (refer to FIG. 2), which controls operations of the AC motor 13. The driving force calculator 7 outputs a driving force command according to the operation conditions of the electric vehicle, thereby controlling the driving force of the AC motor 13.

Even when the present disclosure is applied to the driving system of the electric vehicle such as described above, the current estimation accuracy of the AC motor 13 can be improved while satisfying the demand for the reduction in size and cost by using one current sensor 15 in one AC motor 13.

In the embodiment, the present disclosure is applied to a system including one set of an inverter and an AC motor. Alternatively, the present disclosure can be applied to a system including multiple sets of an inverter and an AC motor.

In the embodiment, the present disclosure is applied to the hybrid vehicle having a structure shown in FIG. 1 and the electric vehicle having a structure shown in FIG. 11. Alternatively, the present disclosure can be applied to an electric vehicle and a hybrid vehicle having another structure. Alternatively, the present disclosure can be applied to a control apparatus for controlling an AC motor used in an apparatus other than an electric vehicle and a hybrid vehicle. 

What is claimed is:
 1. A control apparatus for controlling a three-phase AC motor, the control apparatus comprising: a current sensor configured to detect electric current flowing through one phase of the AC motor, the one phase being defined as a sensor phase; and a current estimation section configured to repeatedly perform a current estimation process in a predetermined cycle, wherein in the current estimation process, a d-axis current estimation value and a q-axis current estimation value in a rotating coordinate system of the AC motor are calculated based on a present current detection value of the sensor phase and a previous current estimation value of another phase of the AC motor previously calculated and stored in memory, the present current detection value being defined as the current presently detected by the current sensor, in the current estimation process, a present current estimation value of each of the sensor phase and the other phase of the AC motor is calculated based on a smoothed d-axis current estimation value and a smoothed q-axis current estimation value into which the d-axis current estimation value and the q-axis current estimation value are respectively smoothed, the current estimation section performs the current estimation process based on a phase lag element of the sensor phase by obtaining dq transformation values of the phase lag element, and adding an inversion of the dq transformation values of the phase lag element to the d-axis current estimation value and the q-axis current estimation value, the phase lag element of the sensor phase is calculated based on a difference between the present current detection value and a previous current estimation value of the sensor phase previously calculated and stored in the memory, and the phase lag element of the sensor phase is calculated based on current information detected by only the current sensor.
 2. The control apparatus according to claim 1, wherein the current estimation section corrects the d-axis current estimation value and the q-axis current estimation value based on the phase lag element of the sensor phase, and the current estimation section calculates the present current estimation value of each of the sensor phase and the other phase by using the corrected d-axis current estimation value and the corrected q-axis current estimation value.
 3. The control apparatus according to claim 2, wherein the current estimation section calculates the dq transformation values of the phase lag element as a d-axis current correction value and a q-axis current correction value in the rotating coordinate system based on the phase lag element of the sensor phase, and the current estimation section corrects the d-axis current estimation value and the q-axis current estimation value by using the d-axis current correction value and the q-axis current correction value, respectively.
 4. The control apparatus according to claim 2, further comprising: a control section configured to control energization of the AC motor based on the d-axis current estimation value and the q-axis current estimation value.
 5. The control apparatus according to claim 3, further comprising: a control section configured to control energization of the AC motor based on the d-axis current estimation value and the q-axis current estimation value.
 6. The control apparatus according to claim 1, wherein the current estimation section corrects the present current detection value based on the phase lag element of the sensor phase, and the current estimation section calculates the d-axis current estimation value and the q-axis current estimation value based on the corrected present current detection value of the sensor phase and the previous current estimation value of the other phase.
 7. The control apparatus according to claim 6, wherein the current estimation section calculates a correction value of the sensor phase based on the phase lag element of the sensor phase, and the current estimation section corrects the present current detection value by using the correction value of the sensor phase.
 8. The control apparatus according to claim 6, further comprising: a control section configured to control energization of the AC motor based on the d-axis current estimation value and the q-axis current estimation value.
 9. The control apparatus according to claim 7, further comprising: a control section configured to control energization of the AC motor based on the d-axis current estimation value and the q-axis current estimation value.
 10. The control apparatus according to claim 1, further comprising: a control section configured to control energization of the AC motor based on the d-axis current estimation value and the q-axis current estimation value. 